Lung cancer is the second most prevalent type of cancer for both men and women in the United States and is the most common cause of cancer death in both sexes. Lung cancer can result from a primary tumor originating in the lung or a secondary tumor which has spread from another organ such as the bowel or breast. The five-year survival rate for lung cancer continues to be poor at 8-15% survival indicating a large unmet need with regard to more effective treatments and better diagnosis. The estimated total lung cancer deaths in the U.S. in 2003 are 157,200 and the total estimated new cases in 2003 are 171,900. Primary lung cancer is divided into three main types; small cell lung cancer; non-small cell lung cancer; and mesothelioma. Small cell lung cancer is also called “Oat Cell” lung cancer because the cancer cells are a distinctive oat shape. There are three types of non-small cell lung cancer. These are grouped together because they behave in a similar way and respond to treatment differently to small cell lung cancer. The three types are squamous cell carcinoma, adenocarcinoma, and large cell carcinoma. Squamous cell cancer develops from the cells that line the airways. Adenocarcinoma also develops from the cells that line the airways. However, adenocarcinoma develops from a particular type of cell that produces mucus (phlegm). Large cell lung cancer has been thus named because the cells look large and rounded when they are viewed under a microscope. Mesothelioma is a rare type of cancer which affects the covering of the lung called the pleura. Mesothelioma is often caused by exposure to asbestos.
Secondary lung cancer is cancer that has started somewhere else in the body (for example, the breast or bowel) and spread to the lungs. Choice of treatment for secondary lung cancer depends on where the cancer started. In other words, cancer that has spread from the breast should respond to breast cancer treatments and cancer that has spread from the bowel should respond to bowel cancer treatments.
The stage of a cancer indicates how far a cancer has spread. Staging is important because treatment is often decided according to the stage of a cancer. The staging is different for non-small cell and for small cell cancers of the lung.
Non-small cell cancer can be divided into four stages. Stage I is very localized cancer with no cancer in the lymph nodes. Stage II cancer has spread to the lymph nodes at the top of the affected lung. Stage III cancer has spread near to where the cancer started. This can be to the chest wall, the covering of the lung (pleura), the middle of the chest (mediastinum) or other lymph nodes. Stage 1V cancer has spread to another part of the body.
Since small cell lung cancer can spread quite early in development of the disease, small cell lung cancers are divided into only two groups. These are: limited disease, that is cancer that can only be seen in one lung and in nearby lymph nodes; and extensive disease, that is cancer that has spread outside the lung to the chest or to other parts of the body. Further, even if spreading is not apparent on the scans, it is likely that some cancer cells will have broken away and traveled through the bloodstream or lymph system. To be safe, it is therefore preferred to treat small cell lung cancers as if they have spread, whether or not secondary cancer is visible. Because surgery is not typically used to treat small cell cancer, except in very early cases, the staging is not as critical as it is with some other types of cancer. Chemotherapy with or without radiotherapy is often employed. The scans and tests done at first will be used later to see how well a patient is responding to treatment.
Procedures used for detecting, diagnosing, monitoring, staging, and prognosticating lung cancer are of critical importance to the outcome of the patient. For example, patients diagnosed with early lung cancer generally have a much greater five-year survival rate as compared to the survival rate for patients diagnosed with distant metastasized lung cancer. New diagnostic methods which are more sensitive and specific for detecting early lung cancer are clearly needed.
Lung cancer patients are closely monitored following initial therapy and during adjuvant therapy to determine response to therapy and to detect persistent or recurrent disease of metastasis. There is clearly a need for a lung cancer marker which is more sensitive and specific in detecting lung cancer, its recurrence, and progression.
Another important step in managing lung cancer is to determine the stage of the patient's disease. Stage determination has potential prognostic value and provides criteria for designing optimal therapy. Generally, pathological staging of lung cancer is preferable over clinical staging because the former gives a more accurate prognosis. However, clinical staging would be preferred were it at least as accurate as pathological staging because it does not depend on an invasive procedure to obtain tissue for pathological evaluation. Staging of lung cancer would be improved by detecting new markers in cells, tissues, or bodily fluids which could differentiate between different stages of invasion.
One promising method for early diagnosis of various forms of cancer is the identification of specific biochemical moieties, termed targets expressed differentially in the cancerous cells. The targets are either cell surface proteins, cytosolic proteins, and/or secreted proteins. Antibodies which will specifically recognize and bind to the targets in the cancerous cells potentially provide powerful tools for the diagnosis and treatment of the particular malignancy.